1. Field of the Invention
The present invention relates generally to suction cups and more specifically to a one-piece suction cup composed of two materials having different properties.
2. Related Art
Suction cups have long been in use to temporarily attach one object to another. Suction cups are not to be confused with vacuum cups, which rely on a device such as a vacuum pump for maintaining a vacuum between the inner surface of the cup and the surface to which the cup is to be attached. The obvious advantage of the suction cup over the vacuum cup is the ease with which the cup may be maneuvered, applied and released. Other advantages include eliminating the need for the vacuum-producing apparatus, thereby reducing cost of manufacture and operation.
Two major problems have plagued users of suction cups from the beginning: early release and early attachment. Early release occurs when a suction cup detaches from a surface earlier than intended. Many attempts have been made to address this problem, including adding an external biasing device to the suction cup to urge its center away from the surface and using a sealant or vacuum grease at the interface between the cup and the surface to enhance the seal. The external biasing device applies an external biasing force to increase the strength of the vacuum within the chamber formed by the cup and the surface, thereby providing a more secure attachment. One such arrangement is disclosed in U.S. Pat. No. 5,133,524 to Liu.
Liu provides a suction cup device comprising a sucking body to be pressed against a surface and a resilient member superimposed above the sucking body that will tend to urge the sucking body away from the surface, which in turn results in the sucking body being more securely attached to the surface. One disadvantage of this approach is that the complexity of the device is increased, thereby increasing both manufacturing costs and likelihood of failure. Another disadvantage is that, while the biasing force increases the strength of the vacuum in the chamber, it does nothing to change the limited "seal zone" of the contact surface.
Early attachment occurs when a suction cup attaches to a surface earlier than intended. Suction cups tend to attach to a surface as soon as contact is made. Early attachment becomes problematic when the location of attachment is important. In many applications it is desirable to slide the suction cup along the surface after contact has been made before activating the cup to achieve final attachment.